The proposed research is concerned with interactions among microbial genetic elements which allow some of these elements to dominate others. Many of the reactions which affect the relative ability of these genetic elements to survive take place at the cell surface. An example of this is the inhibition of T5 bacteriophage replication by the colicin Ib plasmid. Our studies have shown that membrane changes caused by the interaction of phage and plasmid products lead directly to the inhibition. It is hypothesized that a phage protein interacts with a plasmid protein and causes membrane depolarization. We plan to seek direct evidence for this membrane depolarization and to see if this can be attributed to induced cellular ion fluxes. We further plan to identify the phage and plasmid proteins involved by the use of specific mutants and acrylamide gel electrophoresis. In related work, we propose to study the way in which T5 injects its DNA into a potential host cell. This aspect of our research involves the purification, for structure and function studies, of the T5 A1 gene product, and the identification and cellular localization of the T5 A2 protein.